1. Field of the Invention
The present invention relates to a current-to-voltage converting circuit, an optical pickup head apparatus, an apparatus and a method for recording, reproducing or erasing data on an optical disk.
2. Description of the Related Art
Optical memory technologies for recording a large volume of information data on optical disks, each disk having a pattern of pits and used as a high-density, mass-storage recording medium, have now been marketed worldwide in the form of digital audio disks, video disks, text file disks, and data file disks. In particular, digital versatile discs (DVDs) which are recently popularized are optical high-density recordable disks which use a visible light with 650 nm wavelength from a semiconductor laser of a light source. A variety of recording media such as DVD-ROM for read-only operation, DVD-R capable of recording only one time, and DVD-RAM capable of recording a plurality of times are standardized.
FIG. 12 is a schematic view of an optical system of a conventional optical pickup head apparatus for reading data from a DVD-ROM disk as a recording medium. A semiconductor laser 1 emits divergent beam 70 which is linearly polarized and has a wavelength xcex1=650 nm. The beam 70 is reflected on a half-mirror 7 and changed with a path of the beam 70. Subsequently, the beam 70 passes through a collimate lens 8 having 20 mm of a focusing distance, and is collimated to a parallel beam. The beam 70 is then converged by an object lens 9 having 3 mm of a focusing distance, is passed through a transparent substrate 40a of a recording medium 40, and focused on a data recording surface 40b. The aperture of the object lens 9 is limited by an aperture 12, where a numeral aperture (NA) is set to 0.6. The thickness of the transparent substrate 40a is 0.6 mm. The beam 70 reflected on the data recording surface 40b passes through the object lens 9, and the collimate lens 8. Then the beam 70 passes through the half-mirror 7 to be added with an astigmatism, passes through a concave lens 11 of which optical axis is inclined to correct a comma added at the passage through the half-mirror 7, and received by a photo detector 31. An axis 31e is an axis parallel with an image of a track provided on the data recording surface 40b of the recording medium 40 in the beam 70 received on the photo detector 31.
The photodetector 31 has four photo receivers 31a to 31d for outputting current signals I31a to I31d according to amount of received light, respectively. Size of each of photo receivers 31a to 31d is 50 xcexcmxc3x9750 xcexcm. The current signals I31a to I31d are fed into corresponding circuits 50a to 50d of a current-to-voltage converting circuit 50 to be converted into voltage signals V50a to V50d, respectively. The voltage signals V50a to V50d are then released from the optical pickup head apparatus.
A focusing error signal is calculated from the output signals V50a to V50d of the optical pickup head apparatus by an astigmatic method, that is, by a calculation of (V50a+V50c)xe2x88x92(V50b+V50d). A tracking error signal is calculated by a phase difference method of comparing the phases of the signals V50a to V50d when the recording medium is a DVD-ROM or by a push-pull method when the recording medium is a DVD-RAM, that is, by a calculation of (V50a+V50d)xe2x88x92(V50b+V50c). The focusing error signal and the tracking error signal are then amplified to a desired level, and phase-compensated. Subsequently the signals are transferred to actuators 91 and 92 for focusing and tracking control.
FIG. 13 is a diagram of the circuit 50a in the current-to-voltage converting circuit 50. As the four circuits 50a to 50d are identical in construction, the action of the circuit 50a will representatively be described.
The current signal I31a from the photo receiver 31a is received by a terminal P1. The received signal is then converted to a voltage signal by a differential amplifier composed of a pair of transistors Q1 and Q2. A pair of transistors Q4 and Q5 act as a load of the differential amplifier. A voltage at the collector of the transistor Q1 is fed back via a transistor Q7 and a resistor Rf to the base of the transistor Q1. Degree of the conversion of the current signal to the voltage signal in the circuit 50a does not depend on the amplifying factor of each transistor but is determined by the resistor Rf. The voltage signal converted from the current signal is then released as a reference voltage Vc from a terminal P2. A capacitor Cf is used for attenuating poles generated by a parasitic capacitance in the resistor Rf and so on. The base of the transistor Q2 is connected with the reference voltage Vc of the circuit. A voltage between Vcc and GND is 5 V, and a voltage between Vc and GND is 2.5 V. The idling current Ic0 supplied from a current source I0 to the differential amplifier is 1500 xcexcA (The idling current is a collector current which flows the transistor when no signal is input).
Commonly for reproducing data, a DVD-ROM is rotated at 3.49 m/s of linear velocity and a 4.7 GB DVD-RAM is rotated at 8.2 m/s of linear velocity. In a data reproducing apparatuses using DVD-ROM, a technology for rapidly reading data has been developed, and the apparatus are commercialized which can read data substantially 10 or more times faster than an initial products having linear velocity of 3.49 m/s. However, when DVD-RAM is reproduced in such an apparatuses which can reproduce the data faster, there is a problem that the data may not be read accurately since signal-to-noise ratio of the DVD-RAM is lower than that of DVD-ROM. That is, as there is a difference in the optical properties between DVD-ROM and DVD-RAM, it is hard to realize stable reading operation to both types of the recording media.
It is thus an object of the present invention, for eliminating the foregoing drawback and realizing both of the rapid reproduction of DVD-ROM and the stable reproduction of DVD-RAM. The object also is to provide a current-to-voltage converting circuit which is simple in construction and can produce less noises, and an optical pickup head apparatus using such a current-to-voltage converting circuit. It is another object of the present invention to provide an apparatus for recording or reproducing data using the optical pickup head apparatus, and a method of recording or reproducing data implemented with the current-to-voltage converting circuit.
In a first aspect of the invention, a current-to-voltage converting circuit is provided which receives a current signal output from a photodetector outputting a current signal according to amount of received light and converts the received current signal into a voltage signal. The circuit comprises an active element applied with a negative feedback, and a variable current section for varying an idling current which is to be supplied to the active element in accordance with a level of the current signal received from the photodetector or a reproduction speed of the data.
In a second aspect of the invention, a current-to-voltage converting circuit is provided which comprises a current-to-voltage converter which receives a current signal output from a photodetector outputting a current signal according to amount of received light and converts the received current signal into a voltage signal, the current-to-voltage converter comprising an active element applied with a negative feedback, a dummy circuit which has the same structure as the current-to-voltage converter and receives no current signal from the photodetector, a differential operator for performing a differential operation between a signal output from the dummy circuit and a reference signal, a operating section for performing a differential operation or an adding operation, using the voltage signal from the current-to-voltage converter and a signal output from the differential operator, and a current variable section for varying an idling current which is to be supplied to the active element in accordance with a level of the current signal received from the photodetector or a reproduction speed of the data.
In a third aspect of the invention, a current-to-voltage converting circuit is provided which receives a current signal output from a photodetector outputting a current signal according to amount of received light and converts the received current signal into a voltage signal. The circuit comprises a current-to-voltage converter for converting the current signal into the voltage signal, and a variable current section for varying an idling current which is to be supplied to the current-to-voltage converter in accordance with a level of the current signal received from the photodetector or a reproduction speed of the data. In the circuit, a gain to convert a current into a voltage is provided by a negative feedback in which a signal output from the current-to-voltage converter is negatively fed back into an input of the current-to-voltage converter.
In a fourth aspect of the invention, a current-to-voltage converting circuit is provided which receives a current signal output from a photodetector outputting a current signal according to amount of received light and converts the received current signal into a voltage signal. The circuit comprises a current-to-voltage converter for converting the current signal into the voltage signal, an amplifier for receiving the voltage signal from the current-to-voltage converter and amplifying the received voltage signal, and a current variable section for varying an idling current which is to be supplied to the current-to-voltage converter in accordance with a level of the current signal received from the photodetector or a reproduction speed of the data. In the circuit, a gain to convert a current into a voltage is provided by a negative feedback in which a signal output from the amplifier is negatively fed back to the current-to-voltage converter.
In a fifth aspect of the invention, an optical pickup head apparatus is provided which comprises a light source for emitting a laser beam, a light focusing section for focusing the beam which is received from the light source on a recording medium, a beam splitter for splitting the beam which is reflected on the recording medium, a photodetector for receiving the split beam from the beam splitter and releasing a current signal which corresponds to amount of the received beam, and the above current-to-voltage converting circuit for converting the current signal received from the photodetector into a voltage signal.
In a sixth aspect of the invention, an apparatus for recording or reproducing data is provided which comprises the above optical pickup head apparatus, a drive for varying the relative position of the optical pickup head apparatus to a recording medium, and a signal processor for applying a predetermined operation to a signal received from the optical pickup head apparatus to provide a desired data.
In a seventh aspect of the invention, provided is a method of reproducing data from a recording medium by using a current-to-voltage converting circuit for converting a current signal from a photodetector to a voltage signal, the photodetector providing the current signal corresponding to amount of the light reflected on the recording medium, the current-to-voltage converting circuit including an active element applied with a negative feedback and being operable to vary an idling current to be supplied to the active element. The current signal provided from the photodetector has two different levels including a first level and a second level which is smaller than the first level, the idling current to be supplied to the active element has two different currents including a first current (Ic1) and a second current (Ic2) which is smaller than the first current (Ic1). The method comprises detecting the level of the current signal provided from the photodetector, and setting the detected idling current to the first current (Ic1) when the current signal from the photodetector is at the first level, or setting the idling current to the second current (Ic2) when the current signal from the photodetector is at the second level.
In an eighth aspect of the invention, provided is a method of reproducing data from a recording medium by using a current-to-voltage converting circuit for converting a current signal from a photodetector to a voltage signal, the photodetector providing the current signal corresponding to amount of the light reflected on the recording medium, the current-to-voltage converting circuit including an active element applied with a negative feedback and being operable to vary an idling current to be supplied to the active element. The current signal provided from the photodetector is transferred at one of a first transfer rate and a second transfer rate which is slower than the first transfer rate, the idling current to be supplied to the active element has one of a first current (Ic1) and a second current (Ic2) which is smaller than the first current (Ic1). The method comprises detecting the transfer rate of the data, and setting the idling current to the first current (Ic1) when the current signal from the photodetector is transferred at the first transfer rate, or setting the idling current to the second current (Ic2) when the current signal from the photodetector is transferred at the second transfer rate.
According to the present invention, the idling current is selectively determined depending on the reflectance of the recording medium to minimize the generation of noises in the current-to-voltage converting circuit generated from the optical properties of the recording medium so that data read out from the recording medium can be reproduced at optimum conditions. Accordingly, it is possible to perform stably both of reading data at high speed from the recording medium such as DVD-ROM, and reading surely data with a low signal level from the recording medium such as DVD-RAM As a result, the data recording/reproducing apparatus will be improved in the operational reliability,